Pharmacology & the Skin Flashcards Preview

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Flashcards in Pharmacology & the Skin Deck (27)
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1
Q

What are the 2 major routes for drug administration using the skin, and when would you use them?

A

Topical (for local effects) and transdermal/subcutaneous (for systemic effects)

2
Q

What is the most important barrier to drug penetration?

A

The stratum corneum

3
Q

What is the stratum corneum made up of?

A

Consists of corneocytes (hardened, dead, keratinocytes) surrounded by intercellular lipids forming 10 - 30 sheets of tissue (typically 20) that are constantly shed (desquamated) and renewed. Like ‘bricks and mortar’

4
Q

Topical drugs

A

Drug (in a pharmacologically inactive substance, or vehicle) applied directly to the surface of the skin

5
Q

What drives transdermal absorption of topical drugs, and what determines the rate?

A

Diffusion, determined by Fick’s law

6
Q

Fick’s Law

A

J = KpCv - where Kp is the permeability coefficient and Cv is the concentration of drug in the vehicle

7
Q

Inclusion of what, can improve the solubility and absorption of drugs?

A

Excipients eg. propylene glycol and hydration of the skin by occlusion (using ointments or cling film)

8
Q

What do glucocorticosteroids signal via?

A

Nuclear receptors (class 1), specifically GRα

9
Q

Subcutaneous route of administration

A

Drug delivered by a needle inserted into the fatty (adipose) tissue just beneath the surface of the skin. Drug reaches systemic circulation by diffusion into either (i) capillaries, or (ii) lymphatic vessels

10
Q

Why is the skin an attractive route of drug administration for a systemic effect?

A
  • Application is simple and non-sterile (when drug is applied topically)
  • Potentially allows for a steady-state plasma concentration (Cpss) of drug to be achieved over a prolonged period of time
  • Avoids first pass metabolism
  • Drug absorption can be terminated rapidly
11
Q

Transdermal drug delivery

A

Drug is incorporated into an adhesive patch applied to the epidermis. Drug absorption is (partially) controlled by a drug release membrane - occurs by diffusion across cutaneous barrier.

12
Q

For which kind of drugs should transdermal route be used?

A

Most suitable for drugs that are (i) low molecular weight (ii) moderately lipophilic; (iii) potent; (iv) of relatively brief half-life (t½)

13
Q

What are the 2 main groups of strategies to enhance transdermal delivery?

A

Chemical enhancement (Enhancers interact with the lipid matrix of the stratum corneum to increase permeability) and Physical enhancement (eg. iontophoresis, electroporation, sonophoresis, micro needles)

14
Q

Iontophoresis

A

Application of low voltage electrical pulses to the skin via a surface electrode over a prolonged period of time can drive low molecular mass molecules (of the same charge) through the skin.

15
Q

Electroporation

A

Very brief high voltage pulses lead to ‘pore’ formation

16
Q

Sonophoresis

A

Use of ultrasound to increase skin permeability is under investigation for the delivery of some protein drugs (e.g. insulin)

17
Q

What is the purpose of emollients?

A

Enhance rehydration of epidermis

18
Q

What effects do topical corticosteroids have?

A

Vasoconstrictive, anti-inflammatory, anti-proliferative

19
Q

What are the side effects of topical corticosteroids?

A
  • Thinning of the skin, purpura and stretch marks
  • Steroid rosacea (inflammatory rash with papules)
  • Perioral dermatitis (acne-like inflammatory rash)
  • May worsen or mask infections
  • Systemic absorption
  • Tachyphylaxis :decrease in response to anti-inflammatory effects following initial increased response
  • Rebound flare of disease (esp. psoriasis)
20
Q

What are some of the main dermatological uses of topical corticosteroids?

A

Eczema (dermatitis); Psoriasis; Other non-infective inflammatory dermatoses e.g. lichen plants; Keloid scars (usually intralesional)

21
Q

Which antibiotics are mostly used for acne?

A

Clindamycin, erythromycin, tetracycline

22
Q

Which antibiotics is used for rosacea?

A

Metronidazole

23
Q

Which antibiotics are used for impetigo?

A

Mupirocin or fusidic acid

24
Q

What are keratolytics used for?

A

Used to soften keratin in conditions with thickened skin eg. viral warts, hyperkeratotic eczema/psoriasis, corns

25
Q

What is the treatment options for psoriasis?

A

Emollients and a choice of: Coal tar, Vitamin D analogue, Keratolytic, Topical steroid and Dithranol

26
Q

When are calicneurin inhibitors?

A

As alternativess to steroids

27
Q

What is Imiquimod?

A

A topical immune response modulator used for the treatment of some superficial pre-cancerous (actinic keratoses), cancerous skin conditions (superficial basal cell carcinoma) and external genital viral warts